Hello scientists:

Why does hot water sound different when poured than cold water does?

excon

Seems that water reduces weight as it is heated, per the table found here:

Properties Of Hot Water

The mass of water is reduced as it is heated because some of it evaporates into the atmosphere. There is a change in density because as the liquid is heated, the molecules move more rapidly and move farther apart, causing an increase in volume. This also explains the phase change from liquid to gas. The difference in sound could be the steam, it often makes noise.

When you heatt water, air comes out of the cold water.

You faucet which has an aerator, which adds air to the water coming out of the tap, bet you don't perceive a difference.